SepticSceptic:Way back when I did my ESTA it required a 100% pass on the appliance test.
Your analogy of more limited work being conducted by less skilled people exists now, that is why there are ESA and EST qualifications available.
Personally, the 60% pass mark is way too low, considering that they are working with lethal voltages, and customer appliances.
It should be 85% or better, the questions are not that hard ...
A gun license requires 100% pass, and has just as much lethal potential.